Long span screw and nut drives

ABSTRACT

Relatively short coaxial, corotative screw sections are supported by brackets at such intervals as will assure adequate stiffness of the screw against deflection under the loads which it must withstand in service under conditions which a similar screw not supported intermediate its ends could not withstand without deflection. One or more transmission nuts are adapted to run along the screw, or the screw is adapted to run coaxially through the nut or nuts, with free relative passage of the nut and any supporting bracket along the screw. Heavy torque and thrust loads and relatively high speeds can be accommodated. Great practical adaptability and versatility are indicated.

[451 June 20, 1972 LONG SPAN SCREW AND NUT DRIVES FOREIGN PATENTS ORAPPLICATIONS [72] Inventor: John C. Leming, Glen Ellyn, Ill.

[73] Assignee: doizzlrlmlllllGfil' and Tool Corporation, AdprimaryBaminer wmiam E 0.13%

Assistant Examiner--Wesley S. Ratliff, Jr. Attorney-Hill, Sherman,Meroni, Gross & Simpson [22] Filed: 0ct.19, 1970 [21] Appl.No.: 81,996

ABSTRACT Relatively short coaxial, corotative screw sections are sup-[52]U.S.Cl................................................74/89.l5,74/441ported by brackets at such intervals as will assure adequate ....F16h27/02 stiffness of the screw against deflection under the loads which.74/89.l5, 424.8 A, 441 it must withstand in service under conditionswhich a similar screw not supported intermediate its ends could notwithstand without deflection. One or more transmission nuts are adapted[51] lnt.Cl................ [58] Field of References Cited to run alongthe screw, or the screw is adapted to run coaxially through the nut ornuts, with free relative passage of the nut and any supporting bracketalong the screw. Heavy torque and UNITED STATES PATENTS d e t m mm ma 0k6 m 3.] an m mw m. cm W. a g .m m W e P 8 Sd m mi 0 a wo a m b um I kw ce 9 Mm 2 fl 5 mm o In. mm mm tG M M 33 4 M JQQJ mMMm 2 m owm m .w u mWama mey e ue DJKG 8300 3566 9999 nn @0 7 1 5767 0698 ,55 5 mmw 1 2 2 22 P ATENTEDJUHO 1972 3,670, 583

29 Jay/V C 1 E/W/A/G A TTORNE Y5 PATENTEDJMO 1972 SHEET 3 OF 6 INVENTOR.

Jw/A/ C ZZMM/G [fi Q @ATTORNEYS LONG SPAN SCREW AND NUT DRIVES Thisinvention relates to long span screw and nut drives and is moreparticularly concerned with making possible the use of longer screwsthan has heretofore been practical in screw and nut drives.

Long span screws have a tendency to buckle or catenary even when oflarge mass and diameter, and the more slender the screw the greater isthe tendency to deflect laterally from the screw axis under load orpressure whether transverse or endwise. I-Ieretofore this has presentedsevere limitations upon power, force or load transmissions employingscrews and nuts wherein the nuts may travel along the screws or thescrews may travel relative to the nuts depending upon the manner andpurpose of the power transmission. I-Ieretofore certain expedients havebeen proposed to circumvent the problem, such as providing separablehangers to pass the nut thereby as the nut travels along the screw, orby eliminating the nut altogether and substituting rack and pinion,cog'wheel or other even less efiicient forms of transmission. I-lowever,maximum power and low transmission with minimum effort is possible witha screw and nut mechanism.

It is, accordingly, a principal object of the present invention toovercome the foregoing and other disadvantages, defects, inefficiencies,shortcomings and problems in prior structures and to attain importantadvantages and improvements through the novel long span screw and nutdrives exemplified hereinafter.

Another object of the invention is to provide a novel screw and nutdrive wherein the screw will be free from distortion or sagging althoughlong span and requiring that the screw travel uninterruptedly along thespan.

A further object of the invention is to provide a new and improved longspan screw and nut drive in which great resistance is afforded againstinterference or power loss from binding or uneven driving contactbetween the screw and nut.

Still another object of the invention is to provide novel means forsteadying and operating a long span screw andnut drive.

A yet further object of the invention is to provide novel means forsupporting a long span screw in a screw and nut drive.

Yet another object of the invention is to provide new and improved meansfor supporting a long span screw in non-interfering relation withrelative travel of a nut along the screw.

A still further object of the invention is to provide new and improvedmeans for eliminating backlash in a screw and nut drive.

It is also an object of the invention to provide a new and improved longspan screw and nut drive of great versatility as to utility and to meetvarious power transmission requirements.

Other objects, features and advantages of the invention will be readilyapparent from the following description of certain preferred embodimentsthereof, taken in conjunction with the accompanying drawings, althoughvariations and modifications may be effected without departing from thespirit and scope of the novel concepts embodied in the disclosure, andin which:

FIG. 1 is a fragmentary perspective view of a long span screw and nutstructure embodying features of the invention;

FIG. 2 is an enlarged vertical sectional and elevational detail viewtaken substantially along the line Il--Il of FIG. 1;

FIG. 3 is a similar vertical sectional elevational detail view showing amodification;

FIG. 4 is a side elevational view, partially broken away and in sectionof a screw and nut drive showing another modification;

FIG. 5 is a fragmentary longitudinal sectional elevational view througha nut and screw assembly showing a'further modification;

FIG. 6 is a transverse vertical sectional and elevational FIG. 8 is afragmentary longitudinal vertical sectional elevational view through astill further modification showing a nut with an Acme thread;

FIG. 9 is a vertical transverse sectional elevational detail view takensubstantially along the line IX-IX of FIG. 8;

FIG. 10 is a longitudinal vertical sectional elevational detail viewshowing a fluid cushion antifriction screw and nut drive;

FIG. 1 1 is a fragmentary vertical transverse sectional elevational viewof a ball screw nut and screw drive;

FIG. 12 is a top plan view of the arrangement of FIG. 1 1;

FIG. 13 is a side elevational view, partially broken away and in sectionof the arrangement of FIGS. 11 and 12;

FIG. 14 is a fragmentary vertical sectional elevational schematicillustration of an anti-backlash arrangement of the nut and screwdrive;-

FIG. 15 is a fragmentary vertical longitudinal sectional elevationaldetail view showing another modification of the nut and screw drive;

FIG. 16 is a transverse vertical sectional elevational view takensubstantially along the line XVI-XVI of FIG. 15;

FIG. 17 is an illustrative fragmental schematic side elevational viewillustrating an adaptability of the long span screw and nut drive of thepresent invention to attain fixed and variable travel ratios;

FIG. 18 illustrates another arrangement wherein a nut and screw are bothlinearly relatively movable;

FIG. 19 is a schematic illustration of the adaptability for differentialtravel of a plurality of nuts along a long span screw; and

FIG. 20 is a top plan schematic view illustrating the adaptabilityof theprinciples of the present invention to an arrangement wherein the nutmust travel an angular path with a long span screw assembly. 7

According to the principles of the present invention, long span screwand nut drives capable of heavy torque and thrust loads, high speedoperation, as well as great practical adaptability and versatility, areprovided. Linear to rotary, rotary to linear, or combination rotary andlinear motion transmissions or actuations are facilitated. High speedwith low frictional forces is attained simply and economically.Virtually unlimited adaptability for direction or attitude of the screwand nut assembly is feasible, namely, horizontal with underneath supportor hanging support, vertical, or any angular attitude between verticaland horizontal. In the following few representativeexamples, all of therespective screws are rotary in operation while the nuts are heldnon-rotatable relative to the associated screws, and each nut has aclearance slot to pass at least one or more intermediatescrew-supporting brackets. Representative uses are in mechanismactuation, load movers, conveyors, elevators, motion transmissiondevices, drag rigs, transfer gear, and the like.

On reference to FIGS. 1 and 2, a rotary screw 25 has operatively mountedtherewith a non-rotatably coactive nut 27 adapted to travel freelylinearly along the screw. Although it is notintended to limit the typeof screw thread, a desirable form is the square or Acme thread,especially where high torque and thrust load performance arerequired.

For maximum length of span in a screw structure which is of the smallestdiameter and thus slenderness practicable for the intended usefulapplication of the assembly, with complete assurance against bending,buckling, catenary effect, load-induced deflections, speed-inducedwhipping, or other interferences with smooth and reliable performanceover an extended span of whatever length suitable for the particularservice requirements to which put, the screw 25 is provided inrelatively short sections which conform to all of the performancecriteria desired within the limitations of the short screw sectionlength. Each screw section is thoroughly sup ported at each of its endsfor stable concentric rotation by non-rotary supporting means-desirablyin the form of respective brackets 28. Each bracket comprises a spacer29 rigid with a base 30 at one end and a screw-supporting head 31 at theopposite end. Preferably the base 30 is flanged to enable readyattachment as by means of screws 32 to supporting structure such as abeam or frame or runway 33 along which the brackets 28 are mounted insuitable spaced alignment.

In the form shown, the bracket head 31 has a central eye bore 34receptive of a reduced diameter journal portion 35 of the associated endof the screw section or sections supported thereby. About the journaleye 34, the head 31 is of a diameter no greater than the screw threadcrest diameter. In length, the bracket head 31 is sufficient, but nolonger than necessary, to provide adequate journal support for thecoaxial contiguous end portions of two corotatively coupled sections ofthe screw 25.

To receive the screw 25 and the bracket heads 31 therethrough, the bodyof the nut 27 is provided with a longitudinal clearance bore 37 intowhich project screw follower means such as studs 38 complementary to andadapted to ride in the thread grooves of the screw 25 and cooperativewith the screw threads for relative motion transmission, i.e., linearmotion transmitted to the nut 27 by rotation of the screw 25 driven inany suitable manner by any suitable power source, (not shown), or rotarymotion imparted to the screw through the nut 27 by application of anysuitable motivating or power source or means to the nut. The studs 38may be of any suitable form, such as hardened pins mounted radially inthe substantial mass body of the nut 27, anti-friction rollers, or thelike. Means for attachment of the nut 27 to a connecting or couplingdevice such as a yoke, bar, arm, plate, or other member, of associatedmachinery, mechanism, apparatus, may include bolt or screw holes 39 atsuitable placeson or in the body of the nut 27, herein shown asextending into one end face, but which may extend in from either or bothend faces of the nut, or may extend entirely therethrough, or may beprovided where desired on the perimeter of the nut whether thatperimeter is of the generally semi-cylindrical form shown or is of anyother geometric shape desired.

To enable free passage of the nut 27 past the supporting brackets 28,while providing for maximum power transmission connectionbetween thescrew 25 and the nut, as narrow a bracket-clearance slot 40 is providedradially in and throughout the length of the body of the nut extendingfrom the screw clearance bore 37 to the outer perimeter of the nut,complementary to the width of the spacers 29 which are in the form of asnarrow as practicable webs in their transverse dimension but which maybe of any desired width in the longitudinal direction of the screw.Thereby the nut 27 is adapted to bea rugged unit and each of thebrackets 28 is adapted to be a rugged unit, with only inconsequentialarea of the nut bore 37 or screw follower structure of the nutinterrupted by the clearance slot 40. Although the bracket head 31 maybe of an outside diameter small enough to clear the followers 38, formaximum rigidity in the head, it may be desirable to have theconstruction as shown wherein the outside diameter of the head is merelyof slightly smaller diameter than the diameter of the clearance bore 37of the nut and has respective longitudinal grooves 42 therein throughwhich the followers 38 can pass freely, since the nut is non-rotary butmoves rectilinearly past the supporting bracket, with reinforcing ribs43 on the head intervening between the grooves.

While the nut 27 maybe held non-rotary relative to the screw 25 by themeans attached to the nut for driving the nut or to be driven by thenut, as the case may be, a desirable arrangement supporting the nutrelative to the screw in an efiicient concentricity maintaininganti-friction manner comprises a trolley arrangement comprising trolleyoutrigger bars or plates 44 secured by means such as screws 45 to thebody of the nut 27 along each side of the clearance slot 40, andcarrying respective sets of anti-friction rollers 47 running onrespective rails 48 carried by the supporting bar or beam 33. By havingthe rollers 47 in each set engaging with relatively oppositely facingsurfaces of the rails 48, in this instance divergently gibway-likerelated track surfaces, great stability and fairly accurate guidance ofthe nut 27 in the concentric, antifriction relation to the screw 25 isattained.

In FIG. 3 a modified guidance system for the nut 27 is depicted whichmay be preferred for some purposes as affording a more compactarrangement, and especially suitable for installations where it may notbe feasible to mount tracks on other than the screw-supporting brackets.To this end, rail bars 49 of preferably rectangular cross section aremounted on respective shoulders 50 and secured thereto as by means ofscrews 51 at a suitable elevation above the attachment flanges of thebracket base 30. Thereby respective sets of anti-friction rollers 52carried by angle brackets 53 secured as by means of screws 54 to the nut27 are adapted to engage and run on the rails 49 in thoroughlystabilizing, concentricity-maintaining, nut-guiding relation. Anadvantage of the arrangement shown in FIG. 3, in addition to thosealready stated, is that the rollers ,52 are protectively guarded by thedepending roller-carrying portions of the roller-carrying flange members53. It will be understood that the rails 49 extend continuously frombracket-to-bracket and may, if desired, be fonned in sections connectedinalignment, preferably at respective ones of or each of the supportingbrackets 28.

FIG. 4 depicts several features that may be found desirable to meetvarious conditions. One such feature resides in the coupling meansbetween the aligned contiguous ends of the adjacent sections of thescrew 25. To this end, a double ended journal stud 55 has its opposite,threaded end portions threadedly secured into respective threaded axialbores 56 in the screw section ends, with respective locking pins 57secured radially across the bores 56 and through the stud whereby tomaintain the screw sections positively corotative and with therespective ends of the screw threads properly oriented i.e., maintainingconstant lead alignment of the threads, with respect to the gap betweenthe screw ends caused by the intervening bracket head 31 to enableunobstructed reception of the followers 38 by the threads upon leavingone of the screw sections and engaging with the other of the screwsections after travelling across the gap. It will be observed, ofcourse, that the nut 27 is of sufficient length to assure stableengagement of at least one of the screw sections by a plurality of thefollowers 38 while the follower or followers 38 in the lead consideredin the direction of movement of the nut relative to the screw passacross the bracket gap,

and then while the intermediate follower or followers passes the gap,followers are in engagement with both of the screw sections at oppositesides of the gap. Anti-friction bearing means for the journal stud 55may comprise roller bearings 58, while thrust bearings 59 are desirablyprovided between the respective ends of the screw sections and thebracket head 31 to assume end loads.

Another feature in FIG. 4 resides in means for boosting rotary torque ofthe screw 25 at suitable intervals therealong where load conditions,lengths of span, etc., might tend toward undue torsional stresses. Suchintermediate rotary booster means may be of any suitable form, such asgearing 60 comprising a gear train drivingly connected with either thestud 55 or the end of one of the sections of the screw 25 and drivinglycoupled with drive means clear of the nut which is constructed at theslot 40 to clear the gearing in passing thereby. Intermediate gears ofthe train 60 may be rotatably mounted on respective shafts 61 carried bythe bracket fin 29.

An additional feature shown in FIG. 4 comprises a roller passing overrelatively large gaps between the travelling screw section ends and toretain the screw-in relatively frictionless 1 association with thetravelling screw 25. In a desirable arrangement, the roller guideassembly comprises respective their axes normal to the pitch of thethreads of the screw 25, if 5 preferred. Use of the guide rollers 62 isdesirable where it may not be feasible or desired to provide trackguidance for the nut, even though a runner or trolley bar 65 received ina longitudinal peripheral track groove 67 in the nut may be provided toretain the nut against rotation relative to the screw 25.

As shown, especially in and with respect to FIGS. 2,3 and 4, but also inother Figures of the disclosure, the nut 27 is provided with means forsupporting and guiding the nut body to travel along the screw instabilized spaced substantially concentric friction-free relation andlimiting direct contact between the nut and the screw to useful workengagement between the followers and the screw threads.

Various other means than already described may be employed in couplingthe running screw sections together. For example, in FIG. 5 is shown anarrangement wherein the opposite ends of the screw sections are providedwith complementary respective journal portions 68 provided withcomplementary confronting interlocking teeth 69 and journalled in thebracket eye 34. To draw the toothed journal end portions 68 finnlytogether in coaxial relation, a dumbbell coupler 70 is provided havingopposite, threaded heads one of which is provided with fine threads andthe other of which is provided with coarse threads respectivelythreadedly engaged within complementary threaded bores in the screwsections, and accessible for tightening through an axial access bore 71in one or both of the screw sections.

In FIGS. 6 and 7 is shown an arrangement which is especially suitablefor long span assemblies where it may be necessary or desirable fromtime-to-time to release one or more of the screw sections, or where itis not practical to assemble the sections end-to-end through fixed headeyes of the supporting brackets. For this purpose the bracket headcomprises separable complementary parts including a journal receivingsemicylindrical part 31' which is integral with the spacer web 29, and aseparable complementary semi-cylindrical cap head part 31", with thehead parts having complementary mating attachment flanges 72 adapted tobe secured together as by means of screws 73. Within the journal eye 34thus provided, complementary concentric reduced diameter journal endportions 74 on the adjacent ends of the running screw sections arecoupled together by tongue and groove means comprising a coupling tongue75 integral with one of the journal portions 74 fitting slidably in atransverse coupling groove 77 in the adjacent end of the other of thejournal portions 74. Anti-friction roller bearings 78 about the journalportions 74 rotatably journal the journal portions in the eye 34, whilerespective thrust bearings 79 assume end load between a separable splitring spacer 80 and confronting spaced annular shoulders of the brackethead. The split spacer ring 80 maintains the adjacent journal portions74 relatively free from end play. On reference to FIGS. 8 and 9, the nut27 is shown as having the screw follower means in the form of square orAcme threads 81 complementary to and within which the threads of thescrew 25 run for motion transmission. Although if preferred thereinforcing ribs 43 of the bracket head 31 may be omitted, where thehead is provided with such ribs, longitudinal respective clearancegrooves 82 are provided across the threads 81. For alleviation ofexcessive friction between the follower threads of the nut and therunning screw threads, the screw threads or the nut threads or both maybe formed from graphite filled bronze, excessive bearing areas of thethreads may be reduced, lubricant pad areas may be provided within thenut, or other practical lubricating devices may be employed such assuitable lubricator means mounted on the nut.

In FIG. is depicted a completely friction-free square thread drivingconnection between the screw 25 and the nut 27, utilizing a fluidcushion between the cooperating threads.

For this purpose, lubricating fluid, either liquid or gas, is introducedfrom a suitable source through an inlet 83 into a drilled or coreddistributor passage system 84 having substantially equalized dischargeports 85 appropriately located on the side faces of the nut threads 81.Through this means, the screw and nut threads are maintained in spacedsubstantially frictionless floating equilibrium by the lubricatingdynamic fluid introduced under pressure between the threads.

Another driving connection between the nut and screw providingsubstantially frictionless driving thrust is depicted in FIGS. 11-13wherein the screw 25 has half round spiral thread grooves 87 therein,and the nut 27' carries anti-friction follower balls 88 riding in thescrew grooves 87 and running in closed circuit on and in respectiveorbital track grooves 89 provided in a nut body core member 90 carryingthereabout an enclosing complementary coextensive jacket sleeve 91. Aswill be observed, each of the orbital groove tracks 89 has an activefollower run on the inner perimeter of the body 90 complementary inpitch to the pitch of the spiral thread groove 87 of the running screw25'. Escape of the anti-friction follower balls 88 from between thescrew and the body 90 is precluded by the uniform narrow clearance spacetherebetween which is, as clearly evidenced in FIGS. 11 and 13, only asmall fraction of the diameter of the balls. This narrow spacing alsofacilitates movement of the balls across the gap between the threadgroove 87 and respective arcuate transition guide surfaces in the body90 at the respective opposite ends of each of the return run sections ofthe ball orbit grooves 89 located in the outer perimeter of the body 90and closed by the jacket 91. These arcuate groove end portions 92 arelocated as close as practicable to a longitudinal bracket web clearingslot 93 in the otherwise screw-encompassing nut 27 so that the followerballs 88 will be in engagement with the screw to the maximum peripheralextent while making allowance for the bracket clearance slot, similarlyas in all other forms of the invention, typically on the order of 290for the ball follower arrangement, on the order of 280 for the studfollower arrangement, and 320 for the follower thread arrangement.

To enable travel of the ball followers 88 over the intermediate screwsupporting brackets freely and smoothly, each bracket head 31 iscomplementary in diameter to the root diameter of the screw 25 so as to,in effect, provide an extension of the screw in the gap necessitated bythe bracket head between the ends of the screw sections which may becoupled together within and through the head as by means of reduceddiameter terminal journal portions 94 keyed or otherwise coupledtogether as for example by means of matching end keying piece 95. Fortransportation of the follower balls 88 thereacross, the bracket headhas cylindrical surface 97 which is complementary to the root of thethread grooves 87 of the screw and the inner perimeter runs of the balltracking orbit grooves 89 in the nut body 90. Thereby a smoothtransitional running transfer of the follower ball groups fromend-to-end of the adjacent screw sections across the bracket head isattained. Since the follower balls 88 follow closely one upon anotherand run in continuous orbits in the respective groups, extremely smooth,frictionless operation even at high speeds is an important attribute ofthis arrangement.

In some practical applications of the invention, it may be necessary forhighly controlled operation to avoid as nearly as practicable anybacklash play between the screw and nut in running operation. To thisend, a pair of the nuts 27 may, as shown in FIG..14, be operated intandem with loading means therebetween to maintain the followers 38 insnug frictional engagement with the screw threads. Such loading meansare ing of the screw sections in the hanger heads 31, substantially asshown in FIG. 15, may be utilized. To this end, a coupling stud 100 hasrespective opposite, threaded terminal end portions 101 and 102respectively threadedly engaged in complementary threaded bores in theends of the screw sections which are drawn up tight at one end againstan integral collar 103 and at the opposite end against a collar washer104. Means comprising respective pins 105 and 107 lock the screwsections and the stud 100 corotatively in proper alignment. Within thejournal eye 34 of the head 31, the coupling stud 100 is journalledthrough the medium of anti-friction means comprising bearings 108. Inaddition, the eye bore 34 is counterbored at its opposite ends toreceive between the collar 103 at one end and the collar washer 104 atthe other end, and respective confronting thrust shoulders 109 providedon the bracket head by the counterbores, respective preloaded cuppedwasher springs 110. Friction reducing means such as thrust bearings 111are interposed between the springs 110 and one of the shouldering meansin each instance, herein the collars 103 and 104. To protect the preloadand bearing mechanism, respective dust seal rings 112 are protectivelymounted within the outer end portions of the counterbores andrespectively the collar 103 and a cylindrical terminal bearing surface113 on the screw section at the other end of the bracket head. Throughthis arrangement yieldable load in either axial direction is adapted tobe absorbed by the respective springs 110 and the respective supportingbrackets are in a load-sharing relationship. For example, where thereare five brackets a 5,000 pound load may be shared at about 1,000 poundsat each bracket, but in any event will be distributed over the fivebrackets.

Lubricating means may be carried by the nut 27 (FIGS. 8t 16) andconveniently may comprise an attachment on one or both ends of the nutbody. For this purpose, a container 1 14 for lubricants such as oil ismounted on a carrying bracket bar 115 secured as by means of screws 117to the end of the nut body. Lubricant applicator means in the form of afelt or equivalent applicator wick 118 attached to the bracket bar 115receives lubricant from the container 114 through a lubricant duct 119leading from the container 1 l4 and wipingly engages within the threadgrooves of the screw 25 to apply lubricant to the screw threads.

Representative of versatility in use of the long span screw and nutdrive means of the present invention, aside from the more regularrunning of one or more nuts along a rotary screw which is fixed againstany operating axial movement, is the schematically representedarrangement of FIG. 17 wherein the screw 25 is longitudinally shiftablein operation while one or more, in this instance two, nuts 27 aremovable longitudinally along the screw. Means for driving the screw 25may comprise a pulley 120 driven by endless driving means 120a such asflexible belts in a Reeves drive, and with the screw coupled with thepulley through a sliding spline connection 121. The sectional screw 25is supported by intermediate brackets 28 which may be according to anypreferred form such as those hereinbefore described, but mounted formovement with the axially movable screw, represented by anti-frictionroller means 122, by way of example. Longitudinal movement guiding meansrepresented by anti-friction rollers 123. are provided for the nuts 27in this instance. Although both of the nuts 27 may be operated by thescrew to run in the same direction, the arrangement may be, as shown,wherein the nuts are driven to run in opposite directions by having thescrew threads pitched oppositely in different sections of the screw.Thus, with the shaft of the screw 25 rotating in the direcn'on shown bydirectional solid arrows, the left hand nut will run leftward while theright hand nut will run rightward as shown by solid directional arrows,whereas when the screw rotation is reversed the left hand nut will runtoward the right, and the right hand nut will run toward the left, asindicated by the dashed directional arrows. Any suitable device 124 maybe on or connected with the respective nut 27 for motivating desiredmechanism in the running of the respective nut.

Rapid axial traverse of the screw 25 with differential movement of a nuttravelling therealong is attained with the arrangement of FIG. 18,wherein the screw 25 may be driven by the means and runs through astationary nut 27" so that the followers 38 cause the screw to moveaxially at a rate depending on the screw pitch plus rotary speed. At thesame time the free running nut 27 is caused to advance in the respectivedirection directed by the rotating screw at a differential speedgoverned by the screw thread pitch and axial screw travel. In FIG. 19 isshown how differential travel of a plurality of nuts along the screw 25can be attained by variable pitch in the threads of the respective screwsections along the length of the screw. In the illustrative example, theleit hand nut 27 will travel at a slower speed than the right hand nut27 at the same screw speed because the threads along which the left handnut is travelling are of lower pitch than the threads along which theright hand nut is travelling.

As a further example of versatility, there is illustrated in FIG. 20 anarrangement whereby the nuts 27 can be run along an angular track 125 orat least a track in which there are one or more bends. Straight sectionsof the screw 25 extend from each end of the bend in the track with, ifdesired, a flexible shafi coupling 127 between the separated screwsections. A pair of the nuts 27 is connected by a bridging coupling 128which is desirably pivotally attached at its opposite ends as a linkbetween the nuts. By means of the coupling link 128 the nuts are spacedapart greater than the spacing between the separated screw sections sothat at least one of the nuts is in driving relation to one of the screwsections at all times at either end of the bend in the track so thatthere is a constant running connection between the nut train and thescrew 25 to maintain continuous driving relation of the nut train andthe screw assembly. Any preferred running arrangement of the nuts alongthe track 125 may be employed, such as the roller means 52. To avoid anydanger of binding of the nut train along the screw or in transferringbetween the angularly relatedscrew sections the coupling link 128 isdesirably of a preloaded flexible construction, being divided intoseparate sections connected by spring coupler means 129. For thispurpose a shoulder flange 130 is rigid with one of the adjacent linkends and confronts a head shoulder flange 131 rigid with the other suchlink'end. These shoulder flanges are connected in universal relativelymovable relation including limited relative axial movement by preloadedspring means comprising a cupped spring washer 132 between theconfronting spaced faces of the flanges and a cupped spring washer 133between the flange 131 and a compressing and housing cap 134 threadedlydrawn up on an annular marginal housing flange extension 135 on theflange 130 spaced about the perimeter of the flange 131. Overstressingof the springs 131 and 132 may be guarded against by means of spacedstop shoulders 137 and 138 on respectively the flange 130 and the cap134 normally spacedly opposing the margin of the flange 131.

As a further device in smooth, uninterrupted and non-binding running ofthe nuts 27 or either of them onto the screw, the flat, tapered partialthread ends at the ends of the terminal screw sections are desirablyremoved as shown in the fragmentary enlargement within the balloonrepresentation in FIG. 20 and it will be understood to apply to both ofthe terminal section ends shown. As illustrated, the removed end portionof thread is shown in dotted lines with the dotted followerrepresentation showing how the follower might strike the partial flatend of the thread while the full line showing of the followerdemonstrates how the follower moves directly into the helix of thegroove without interruption. Preferably, the leading end of the threadis tapered slightly inwardly as shown. This feature will also be foundvaluable in other adaptations of the nut and screw assembly where it isdesirable to run the nut off of and onto the end of the screw for anyreason while the screw continues to rotate uninterruptedly. This featureis also desirable where as in FIG. 17 there is a reversal of the screwhelix from section to section, or where as in FIG. 19 there is adifierence in helix pitch from section to section.

It will be apparent that the arrangement of FIG. 20 lends itself tonumerous practical adaptations wherein not only will the spacedlink-coupled nuts be capable of linear, though angular running, but mayalso run along parallel or even nonparallel separate directions with thelink 128 serving as a supporting medium in a conveyor or otherapparatus. The nuts either jointly or individually may be switched fromone track to another track. Numerous other permutations will readilysuggest themselves.

it will be understood that variations and modifications may be effectedwithout departing from the spirit and scope of the novel concepts ofthis invention.

1 claim:

1. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section; and

means supporting and guiding said nut body to travel along said screw instabilized spaced substantially concentric friction-free relation andlimiting direct contact between the nut and the screw to useful workengagement between the followers and the screw threads.

2. An assembly according to claim 1, said nut supporting and guidingmeans comprising a roller guide assembly on at least one end of the nutbody and riding on the crest of the screw threads and being of a lengthto bridge across the adjacent ends of the screw sections for continuityof motion transmission engagement of said follower means with the screwthreads of the sections during said transfer.

3. An assembly according to claim 1, said non-rotary supporting meanscomprising a bracket having a base and a journal head with a narrowerspacer web between said base and head, said head being of no greaterdiameter than said screw sections and said web being substantiallynarrower than the diameter of said screw sections, said nut slot beingof a width which is only slightly greater than the width of said web,said nut supporting and guiding means including trolley outriggel'sfixed to and projecting laterally from the nut body and track means withwhich the Outriggers have antifriction engages ment.

4. An assembly according to claim 1, said nut supporting and guidingmeans including track means and a plurality of rollers carried by thenut body and running along the track means for maintaining the nut innon-rotary relation to the screw but permitting free axial movement ofthe nut along the screw.

5. An assembly according to claim 1, wherein said support.

7. An assembly according to claim 5, wherein said rail means are carriedby said non-rotary supporting means and provide three track surfaces,said trolley means having three rollers running along said tracksurfaces.

8. An assembly according to claim 1, wherein saidscrew sections havecoupling means maintaining constant lead alignment of the threads of thesections.

9. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

said supporting means comprising a bracket having a base and a journalhead with a narrower spacer web between said base and head;

said head being of no greater diameter than said screw sections and saidweb being substantially narrower than the diameter of said screwsections;

said nut slot being of a width which is only slightly greater than thewidth of said web; and

said bracket head having grooves therein through which said followermeans are adapted to travel as the nut transfers fromsection-to-section.

10. A long span screw and nut drive assembly, comprising: a screw havingcoaxial corotative screw sections with thread grooves of the sectionsoperatively aligned, such sections being individually capable ofwithstanding load and torque stresses for an intended purpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

said supporting means comprising a journal head between adjacent endportions of said screw sections,

journal means in said head and corotatively coupling the screw sections;

said journal means comprising respective journal extensions on the screwsection end portions having interlocking means for corotationalassembly; and

connector means in the screw end portions maintaining the coupledrelationship.

11. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journailing, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from v section-to-section; and

said supporting means including a journal head comprising a separablecap enabling lateral removal of the screw sections when the cap isremoved.

12. A long span screw and nut drive assembly, comprising:

a screw having a plurality of coaxial corotative screw sections withthread grooves of the sections operatively aligned, such sections beingindividually capable of withstanding load and torque stresses for anintended pura plurality of respective non-rotary supporting meansbetween, and rotatably journalling, said screw sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section; and

means cooperative with said sections and the supporting means providingfor axial load sharing at the respective supporting means along thelength of the screw.

13. An assembly according to claim 12, said supporting means in eachinstance comprising a journal head, and the load-sharing meanscomprising preloaded cupped spring washer means under yieldablecompression between spaced confronting shoulders on respectively thejournal heads and the screw sections.

14. A longspan screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections withthread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal'slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section; and

said follower means comprising follower studs projecting radially froman inner perimeter of the nut into the screw threads.

15. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose; i

non-rotary supporting means between, and rotatably joursaid nut bodybeing provided with alongitudinal slot to clear said supporting means inrelative passing of the nut and the supporting means during relativeaxial movement of the screw and the nut requiring transfer of the nutfrom section-to-section; said thread grooves being provided by squarethreads on the sections; said follower means of the nut comprisingcomplementary square threads interfitting with the screw sectionthreads; and means providing anti-friction dynamic fluid cushion betweenthe screw threads and the nut threads.

16. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew secu'ons;

v a nut non-rotatably coactive with said screw and having a bodycarrying follower means operatively engaging the screw threads in saidgrooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

said follower means comprising anti-friction ball trains; and

a plurality of individual orbital raceways in the nut for said balltrains and having arcuate ball return surfaces adjacent to said slot.

17. An assembly according to claim 16, in which said nut comprises abody having said raceways, and a jacket about said body cooperating withthe body in closing a run of said raceways.

l8. Along span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section; and

means carried-by the nut for applying lubrication in said threadgrooves.

19. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

track means comprising a bar for maintaining the nut in ,a nutnon-rotat'ably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section; fixedly mounted track meansfor maintaining the nut in nonrotary relation to the screw butpermitting free axial v movement of the nut along the screw; and saidnut having anti-friction roller means riding along the track means. 21.A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose; non-rotary supporting means between, and rotatably journailing,said screw sections; a pair of nuts non-rotatably coactive with saidscrew and each having a body carrying follower means operativel engagingthe screw threads in said grooves;

said nut bodies being provided with respective longitudinal slots toclear said supporting means in relative passing of the nuts and thesupporting means during relative axial movement of the screw and thenuts requiring transfer of the nuts from section-to-section; and

means connecting the nuts and applying a relative axial loadtherebetween to substantially eliminate axial play between the nutfollowers and the screw sections in said thread grooves.

22. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

means for driving said screw rotatably and enabling axial move-ment ofthe screw;

said supporting means being axially movable with the screw;

and

said nut being axially movable along the screw responsive to motiontransmission coaction between said follower means and said screwsections within said thread grooves.

23. An assembly according to claim 22, including a fixed nut operativelyengaging said screw and effecting longitudinal movement of the screw asthe screw is driven rotatably.

24. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

a plurality of separate ones of the nuts each having followersoperatively engaging in the thread grooves of the sections and eachhaving a slot to pass said supporting means;

said thread grooves of different ones of the sections being reverse inoperation so that as the screw rotates in one direction, the nuts aredriven to move axially therealon in opposite longitudinal directions.

25. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves; I

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from tion along the screw said thread grooves of therespective sections being of different pitch to effect differentialaxial travel of the nuts along the screw in the rotation of the screw.

26. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

track means for guiding the nut axially along the screw;

said track means having an angular bend therein with portions of thescrew separated by the length of said bend; and

means for effecting continuous travel transition of the nut across thespace between the screw portions.

27. An assembly according to claim 26, in which said lastmentioned meanscomprise a second similar nut; means connecting the nuts together inspaced relation greater than the spacing between said screw portions,and means for coordinating rotation of said screw portions.

28. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section;

primary driving means for the screw; and

booster driving means associated with said supporting means.

29. A long span screw and nut drive assembly, comprising:

a screw having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose;

non-rotary supporting means between, and rotatably journalling, saidscrew sections;

a nut non-rotatably coactive with said screw and having a body carryingfollower means operatively engaging the screw threads in said grooves;

said nut body being provided with a longitudinal slot to clear saidsupporting means in relative passing of the nut and the supporting meansduring relative axial movement of the screw and the nut requiringtransfer of the nut from section-to-section; and

an end on one of the screw sections having at least one thread ending atsuch end, said thread end being free from partial thread so that thefollower means will pass directly into a thread groove withoutinterference.

l i l

1. A long span screw and nut drive assembly, comprising: a screw havingcoaxial corotative screw sections with thread grooves of the sectionsoperatively aligned, such sections being individually capable ofwithstanding load and torque stresses for an intended purpose;non-rotary supporting means between, and rotatably journalling, saidscrew sections; a nut non-rotatably coactive with said screw and havinga body carrying follower means operatively engaging the screw threads insaid grooves; said nut body being provided with a longitudinal slot toclear said supporting means in relative passing of the nut and thesupporting means during relative axial movement of the screw and the nutrequiring transfer of the nut from section-tosection; and meanssupporting and guiding said nut body to travel along said screw instabilized spaced substantially concentric frictionfree relation andlimiting direct contact between the nut and the screw to useful workengagement between the followers and the screw threads.
 2. An assemblyaccording to claim 1, said nut supporting and guiding means comprising aroller guide assembly on at least one end of the nut body and riding onthe crest of the screw threads and being of a length to bridge acrossthe adjacent ends of the screw sections for continuity of motiontransmission engagement of said follower means with the screw threads ofthe sections during said transfer.
 3. An assembly according to claim 1,said non-rotary supporting means comprising a bracket having a base anda journal head with a narrower spacer web between said base and head,said head being of no greater diameter than said screw sections and saidweb being substantially narrower than the diameter of said screwsections, said nut slot being of a width which is only slightly greaterthan the width of said web, said nut supporting and guiding meansincluding trolley outriggers fixed to and projecting laterally from thenut body and track means with which the outriggers have antifrictionengagement.
 4. An assembly according to claim 1, said nut supporting andguiding means including track means and a plurality of rollers carriedby the nut body and running along the track means for maintaining thenut in non-rotary relation to the screw but permitting free axialmovement of the nut along the screw.
 5. An assembly according to claim1, wherein said supporting and guiding means comprise trolley means onsaid nut body, rail means extending parallel to said screw, and rollerscarried by said trolley means and running along said rail means.
 6. Anassembly according to claim 5, wherein said rail means have divergentlygibway-like related track surfaces along which the rollers run.
 7. Anassembly according to claim 5, wherein said rail means are carried bysaid non-rotary supporting means and provide three track surfaces, saidtrolley means having three rollers running along said track surfaces. 8.An assembly according to claim 1, wherein said screw sections havecoupling means maintaining constant lead alignment of the threads of thesections.
 9. A long span screw and nut drive assembly, comprising: ascrew having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose; non-rotary supporting means between, and rotatably journalling,said screw sections; a nut non-rotatably coactive with said screw andhaving a body carrying follower means operatively engaging the screwthreads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means During relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;said supporting means comprising a bracket having a base and a journalhead with a narrower spacer web between said base and head; said headbeing of no greater diameter than said screw sections and said web beingsubstantially narrower than the diameter of said screw sections; saidnut slot being of a width which is only slightly greater than the widthof said web; and said bracket head having grooves therein through whichsaid follower means are adapted to travel as the nut transfers fromsection-to-section.
 10. A long span screw and nut drive assembly,comprising: a screw having coaxial corotative screw sections with threadgrooves of the sections operatively aligned, such sections beingindividually capable of withstanding load and torque stresses for anintended purpose; non-rotary supporting means between, and rotatablyjournalling, said screw sections; a nut non-rotatably coactive with saidscrew and having a body carrying follower means operatively engaging thescrew threads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;said supporting means comprising a journal head between adjacent endportions of said screw sections, journal means in said head andcorotatively coupling the screw sections; said journal means comprisingrespective journal extensions on the screw section end portions havinginterlocking means for corotational assembly; and connector means in thescrew end portions maintaining the coupled relationship.
 11. A long spanscrew and nut drive assembly, comprising: a screw having coaxialcorotative screw sections with thread grooves of the sectionsoperatively aligned, such sections being individually capable ofwithstanding load and torque stresses for an intended purpose;non-rotary supporting means between, and rotatably journalling, saidscrew sections; a nut non-rotatably coactive with said screw and havinga body carrying follower means operatively engaging the screw threads insaid grooves; said nut body being provided with a longitudinal slot toclear said supporting means in relative passing of the nut and thesupporting means during relative axial movement of the screw and the nutrequiring transfer of the nut from section-to-section; and saidsupporting means including a journal head comprising a separable capenabling lateral removal of the screw sections when the cap is removed.12. A long span screw and nut drive assembly, comprising: a screw havinga plurality of coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose; a plurality of respective non-rotary supporting means between,and rotatably journalling, said screw sections; a nut non-rotatablycoactive with said screw and having a body carrying follower meansoperatively engaging the screw threads in said grooves; said nut bodybeing provided with a longitudinal slot to clear said supporting meansin relative passing of the nut and the supporting means during relativeaxial movement of the screw and the nut requiring transfer of the nutfrom section-to-section; and means cooperative with said sections andthe supporting means providing for axial load sharing at the respectivesupporting means along the length of the screw.
 13. An assemblyaccording to claim 12, said supporting means in each instance comprisinga journal head, and the load-sharing means comprising preloaded cuppedspring washer means under yieldable compression between spacedconfronting shoulders on respectively the journal heads and The screwsections.
 14. A long span screw and nut drive assembly, comprising: ascrew having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose; non-rotary supporting means between, and rotatably journalling,said screw sections; a nut non-rotatably coactive with said screw andhaving a body carrying follower means operatively engaging the screwthreads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;and said follower means comprising follower studs projecting radiallyfrom an inner perimeter of the nut into the screw threads.
 15. A longspan screw and nut drive assembly, comprising: a screw having coaxialcorotative screw sections with thread grooves of the sectionsoperatively aligned, such sections being individually capable ofwithstanding load and torque stresses for an intended purpose;non-rotary supporting means between, and rotatably journalling, saidscrew sections; a nut non-rotatably coactive with said screw and havinga body carrying follower means operatively engaging the screw threads insaid grooves; said nut body being provided with a longitudinal slot toclear said supporting means in relative passing of the nut and thesupporting means during relative axial movement of the screw and the nutrequiring transfer of the nut from section-to-section; said threadgrooves being provided by square threads on the sections; said followermeans of the nut comprising complementary square threads interfittingwith the screw section threads; and means providing anti-frictiondynamic fluid cushion between the screw threads and the nut threads. 16.A long span screw and nut drive assembly, comprising: a screw havingcoaxial corotative screw sections with thread grooves of the sectionsoperatively aligned, such sections being individually capable ofwithstanding load and torque stresses for an intended purpose;non-rotary supporting means between, and rotatably journalling, saidscrew sections; a nut non-rotatably coactive with said screw and havinga body carrying follower means operatively engaging the screw threads insaid grooves; said nut body being provided with a longitudinal slot toclear said supporting means in relative passing of the nut and thesupporting means during relative axial movement of the screw and the nutrequiring transfer of the nut from section-to-section; said followermeans comprising anti-friction ball trains; and a plurality ofindividual orbital raceways in the nut for said ball trains and havingarcuate ball return surfaces adjacent to said slot.
 17. An assemblyaccording to claim 16, in which said nut comprises a body having saidraceways, and a jacket about said body cooperating with the body inclosing a run of said raceways.
 18. A long span screw and nut driveassembly, comprising: a screw having coaxial corotative screw sectionswith thread grooves of the sections operatively aligned, such sectionsbeing individually capable of withstanding load and torque stresses foran intended purpose; non-rotary supporting means between, and rotatablyjournalling, said screw sections; a nut non-rotatably coactive with saidscrew and having a body carrying follower means operatively engaging thescrew threads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;and means carried by the nut for applying lubrication in said threadgrooves.
 19. A lonG span screw and nut drive assembly, comprising: ascrew having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose; non-rotary supporting means between, and rotatably journalling,said screw sections; a nut non-rotatably coactive with said screw andhaving a body carrying follower means operatively engaging the screwthreads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;track means comprising a bar for maintaining the nut in non-rotaryrelation to the screw but permitting free axial movement of the nutalong the screw; and said nut having a track groove within which the baris received.
 20. A long span screw and nut drive assembly, comprising: ascrew having coaxial corotative screw sections with thread grooves ofthe sections operatively aligned, such sections being individuallycapable of withstanding load and torque stresses for an intendedpurpose; non-rotary supporting means between, and rotatably journalling,said screw sections; a nut non-rotatably coactive with said screw andhaving a body carrying follower means operatively engaging the screwthreads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;fixedly mounted track means for maintaining the nut in non-rotaryrelation to the screw but permitting free axial movement of the nutalong the screw; and said nut having anti-friction roller means ridingalong the track means.
 21. A long span screw and nut drive assembly,comprising: a screw having coaxial corotative screw sections with threadgrooves of the sections operatively aligned, such sections beingindividually capable of withstanding load and torque stresses for anintended purpose; non-rotary supporting means between, and rotatablyjournalling, said screw sections; a pair of nuts non-rotatably coactivewith said screw and each having a body carrying follower meansoperatively engaging the screw threads in said grooves; said nut bodiesbeing provided with respective longitudinal slots to clear saidsupporting means in relative passing of the nuts and the supportingmeans during relative axial movement of the screw and the nuts requiringtransfer of the nuts from section-to-section; and means connecting thenuts and applying a relative axial load therebetween to substantiallyeliminate axial play between the nut followers and the screw sections insaid thread grooves.
 22. A long span screw and nut drive assembly,comprising: a screw having coaxial corotative screw sections with threadgrooves of the sections operatively aligned, such sections beingindividually capable of withstanding load and torque stresses for anintended purpose; non-rotary supporting means between, and rotatablyjournalling, said screw sections; a nut non-rotatably coactive with saidscrew and having a body carrying follower means operatively engaging thescrew threads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;means for driving said screw rotatably and enabling axial movement ofthe screw; said supporting means being axially movable with the screw;and said nut being axially movable along the screw responsive to motiontransmission coaction between said follower means And said screwsections within said thread grooves.
 23. An assembly according to claim22, including a fixed nut operatively engaging said screw and effectinglongitudinal movement of the screw as the screw is driven rotatably. 24.A long span screw and nut drive assembly, comprising: a screw havingcoaxial corotative screw sections with thread grooves of the sectionsoperatively aligned, such sections being individually capable ofwithstanding load and torque stresses for an intended purpose;non-rotary supporting means between, and rotatably journalling, saidscrew sections; a nut non-rotatably coactive with said screw and havinga body carrying follower means operatively engaging the screw threads insaid grooves; said nut body being provided with a longitudinal slot toclear said supporting means in relative passing of the nut and thesupporting means during relative axial movement of the screw and the nutrequiring transfer of the nut from section-to-section; a plurality ofseparate ones of the nuts each having followers operatively engaging inthe thread grooves of the sections and each having a slot to pass saidsupporting means; said thread grooves of different ones of the sectionsbeing reverse in operation so that as the screw rotates in onedirection, the nuts are driven to move axially therealong in oppositelongitudinal directions.
 25. A long span screw and nut drive assembly,comprising: a screw having coaxial corotative screw sections with threadgrooves of the sections operatively aligned, such sections beingindividually capable of withstanding load and torque stresses for anintended purpose; non-rotary supporting means between, and rotatablyjournalling, said screw sections; a nut non-rotatably coactive with saidscrew and having a body carrying follower means operatively engaging thescrew threads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;including a plurality of similar nuts mounted in running relation alongthe screw; said thread grooves of the respective sections being ofdifferent pitch to effect differential axial travel of the nuts alongthe screw in the rotation of the screw.
 26. A long span screw and nutdrive assembly, comprising: a screw having coaxial corotative screwsections with thread grooves of the sections operatively aligned, suchsections being individually capable of withstanding load and torquestresses for an intended purpose; non-rotary supporting means between,and rotatably journalling, said screw sections; a nut non-rotatablycoactive with said screw and having a body carrying follower meansoperatively engaging the screw threads in said grooves; said nut bodybeing provided with a longitudinal slot to clear said supporting meansin relative passing of the nut and the supporting means during relativeaxial movement of the screw and the nut requiring transfer of the nutfrom section-to-section; track means for guiding the nut axially alongthe screw; said track means having an angular bend therein with portionsof the screw separated by the length of said bend; and means foreffecting continuous travel transition of the nut across the spacebetween the screw portions.
 27. An assembly according to claim 26, inwhich said last-mentioned means comprise a second similar nut; meansconnecting the nuts together in spaced relation greater than the spacingbetween said screw portions, and means for coordinating rotation of saidscrew portions.
 28. A long span screw and nut drive assembly,comprising: a screw having coaxial corotative screw sections with threadgrooves of the sections operatively aligned, such sections beingindividually capable of withstanding load and torque stresses for anintended purpose; non-rotary supporting means between, and rotatablyjournalling, said screw sections; a nut non-rotatably coactive with saidscrew and having a body carrying follower means operatively engaging thescrew threads in said grooves; said nut body being provided with alongitudinal slot to clear said supporting means in relative passing ofthe nut and the supporting means during relative axial movement of thescrew and the nut requiring transfer of the nut from section-to-section;primary driving means for the screw; and booster driving meansassociated with said supporting means.
 29. A long span screw and nutdrive assembly, comprising: a screw having coaxial corotative screwsections with thread grooves of the sections operatively aligned, suchsections being individually capable of withstanding load and torquestresses for an intended purpose; non-rotary supporting means between,and rotatably journalling, said screw sections; a nut non-rotatablycoactive with said screw and having a body carrying follower meansoperatively engaging the screw threads in said grooves; said nut bodybeing provided with a longitudinal slot to clear said supporting meansin relative passing of the nut and the supporting means during relativeaxial movement of the screw and the nut requiring transfer of the nutfrom section-to-section; and an end on one of the screw sections havingat least one thread ending at such end, said thread end being free frompartial thread so that the follower means will pass directly into athread groove without interference.